JP4900678B2 - Aperture device having ND filter and optical apparatus - Google Patents

Description

The present invention relates to a diaphragm device and optical instruments having a N D filter.

  2. Description of the Related Art Conventionally, in an imaging apparatus such as a video camera, an ND (Neutral Density) filter is used for a light amount diaphragm device, so that the aperture aperture is prevented from becoming extremely small even in a bright field, and a hunting phenomenon, a light diffraction phenomenon, etc. To prevent this.

As a specific example of the light quantity reduction device using the ND filter, for example, a device using a step ND filter in which the density is changed in multiple stages shown in Patent Document 1 is known.
Further, there is known one using a gradation ND filter in which the density change region shown in Patent Document 2 is long and the density changes steplessly.
JP 2002-277612 A Japanese Patent No. 03621941

By the way, when a conventional ND filter is used in the light quantity diaphragm device, quite complicated control is required.
Specifically, the difference between the transmitted light quantity of the transmitted light quantity of the light quantity diaphragm device at a certain point in time and the appropriate transmitted light quantity is calculated, and the aperture or ND filter is operated according to a predetermined algorithm. Therefore, an appropriate exposure amount can be obtained.
Also, in order to obtain optimal exposure or optimal exposure compensation, the control algorithm is changed depending on the subject brightness, and the zoom lens use focal length and lens focus position (distance) information are also used as control parameters depending on the model. .
Thus, the control includes extremely complicated control elements.
Furthermore, when changing the transmitted light amount by changing the density of the ND filter, the aperture diameter of the stop is often small, and a slight difference in density of the ND filter results in a large difference in transmitted light amount.
Therefore, when controlling the amount of light using an ND filter, particularly when using a gradation ND filter whose density continuously changes at any position according to the amount of operation, the relationship between the amount of operation and the amount of transmitted light is related. However, it becomes extremely difficult.

On the other hand, in the step ND filter, it is only necessary to pay attention to the position of the density switching portion, in other words, the ratio of the area of the low density portion to the area of the dark portion. The control is relatively easy.
However, in the step ND filter, when the light is considered as a wave, the phase is shifted due to the difference in the optical film thickness of the ND film of the passing filter, and the image quality is affected. That is, as disclosed in Japanese Patent Application Laid-Open No. 2004-253892 (see page 22 and FIG. 24), the transmission wavefront phase difference affects the image quality.
This is because the type of step ND filter that obtains a different density by changing the thickness of the film having the same refractive index, the phase of the light that has passed through the region having a different density depending on the film thickness By deviating and interfering with each other to deteriorate the resolution. The effect is greatest when the areas of different concentrations are equal. In this state, when the difference between the film thicknesses, that is, the transmitted wavefront phase difference is changed, the MTF (modulation transfer function) value representing the on-axis optical performance varies with the period λ.

As the phase difference between the two increases, the MTF decreases, the extreme value is increased at the phase difference 2λ / 4, then increased, and the extreme value is decreased again at 4λ / 4, and the extreme value is decreased at 6λ / 4. It turns to rise and shows an extreme value again at 8λ / 4.
Further, when comparing the step ND filter and the gradation ND filter, in the step ND filter, particularly when the density difference is large, the density change at the density boundary part is discontinuous, so that diffraction occurs and the image quality deteriorates.
As described above, the step ND filter has a problem of diffraction and transmitted wavefront phase difference, and the image quality may be inferior to that of the gradation ND filter.
However, the step ND filter is easier than the gradation ND filter in controlling the light quantity reduction device, and the development of the control program is often possible in a short period of time.

In view of the above problems, the control of the aperture diaphragm device, while being relatively easy to step ND filter, a diaphragm device and a N D filter Do that is possible to reduce deterioration in optical performance The purpose is to provide optical equipment.

The present invention, in order to solve the above problems, there is provided a diaphragm device and optical instruments having a N D filter constituted as follows.
The diaphragm device of the present invention includes a diaphragm member that forms an opening;
An ND filter for attenuating the amount of light passing through the opening;
The ND filter is
A first region having a certain concentration of ND film;
A second region having an ND film having a constant concentration different from that of the first region;
A concentration change region provided between the first region and the second region;
The concentration changing region has an ND film whose concentration continuously changes from the concentration of the first region to the concentration of the second region,
The width of the concentration change region is such that when the areas of the first region and the second region are the same in the opening, the area of the concentration change region in the opening is 20% of the area of the opening. The width is set to be as follows.
An optical apparatus of the present invention includes an optical system including a diaphragm Ri device described above,
A solid-state image sensor that receives an image formed by the optical system is provided.

According to the present invention, control of the aperture diaphragm device is relatively simple as the conventional step ND filter, moreover is possible to realize a throttle device and an optical device having a N D filter has little decrease in optical performance it can.

  The best mode for carrying out the present invention will be described by the following examples.

The light quantity adjustment ND filter applied to the diaphragm device of this embodiment will be described with reference to FIG.

1A to 1C, 10 is a transparent substrate, and 11a to 11d are ND films each formed of a multilayer film.
In the ND filter of this embodiment, the concentration is continuously between the region 1 having an ND film having a single concentration (constant concentration) and the region 2 having an ND film having a single concentration different from the ND region 1. A density change region having a changing ND film is provided.
FIG. 1A is an example in which the above-described configuration is realized by forming the ND film 11 a only on one surface of the transparent substrate 10.
FIG. 1B is an example in which the above configuration is realized by forming ND films 11 b and 11 c on both surfaces of the transparent substrate 10.
FIG. 1C is a modification of the example of FIG. 1A, in which a concentration change region is formed between the region 2 and a region with a transmittance of 100% (a region where no ND film is formed). It is. In FIGS. 1A to 1C, the thickness of the ND film and the base material is shown in an exaggerated shape.

Concerning the concentration structure, the single concentration region may be a multi-concentration with 3 or more regions, but 4 to 5 regions are considered to be the limit in consideration of the stress of the substrate and the film.
Since the concentration of each region may be a desired concentration, in this embodiment, the region 1 has a structure with a concentration D = 1.0 and a film thickness of 500 nm, and the region 2 has a structure with a concentration D = 0.5 and a film thickness of 250 nm. Will be explained.
Here, the density D = −log ₁₀ (transmittance), D = 1.0 when the transmittance is 10%, and D = 0.5 when the transmittance is 32%.
As described above, when the density D of the region 1 is set to 1.0 and the density D of the region 2 is set to 0.5, the phase difference of the transmitted wave front between the region 1 and the region 2 is approximately λ / 2.
This is an unfavorable relationship for the transmitted wavefront phase difference, but the concentration is a value that has been used as a conventional step ND filter, and is a relationship of the concentration required as a practical step ND filter.

  The lamination of the ND film has a structure in which a single concentration film of D = 0.5 is formed twice by vapor deposition. As described above, FIG. 1A shows an example in which such a single concentration film is formed twice on one side of the transparent resin substrate 10. FIG. 1B shows an example in which a single-concentration film is formed once on one side of the transparent substrate 10 and formed once more on the other side. FIG. 1C shows an optimum structure in a case where the ND filter is inserted into a part of the aperture opening. As shown in FIG. 1C, it is possible to suppress image degradation by continuously changing the density of the cut end surface of the region 2 as well.

In such a configuration, if the density change is discontinuous at the boundary between two different density regions, diffraction due to a rapid density difference occurs.
Further, depending on the ratio of the areas, the influence of the transmitted wavefront phase difference becomes large, which causes image quality deterioration (decrease in resolution).
The transmitted wavefront phase difference is generated due to the relationship between the thicknesses of the two even if the boundary is not particularly discontinuous. In particular, in the relationship between two density regions, the image quality degradation is greatest when the ratio of the areas of both is 50%.
In the present embodiment, it is possible to alleviate image quality degradation by providing a region having a certain width in which the density continuously changes between the two density regions.
For example, when the ratio of the area of two single density regions is 40%, the image quality deterioration due to the transmitted wavefront phase difference is alleviated by providing a density change region having a ratio of 20%. Is possible.

As described above, according to the ND filter of this embodiment, even if the density step between the two single density regions is large, the influence of diffraction can be reduced.
Moreover, even when the transmitted wavefront phase difference is in a relationship of degrading the resolution as in the case of 2λ / 4 or 6λ / 4, it is possible to alleviate the degradation of the resolution.
At the same time, by making the width of the density change area not to exceed the predetermined upper limit, it becomes possible to perform control equivalent to the control of the light quantity diaphragm device using the conventional step ND filter, and the load of development of the control system is reduced. It becomes possible to reduce.
In addition, when developing a model equipped with either the conventional step ND filter or the ND filter according to the present invention, the control circuit of the light quantity diaphragm device may be the same.
Therefore, it is possible to achieve labor saving in development and manufacturing of the control circuit.

Next, a manufacturing method of the ND filter having the above-described density change region will be described. In this implementation, an ND filter by a vacuum deposition method was manufactured.
FIG. 2 is a simplified view of the inside of the chamber in the vacuum deposition apparatus.
In FIG. 2A, 12 is a substrate on which a film is formed, 15 is a vapor deposition umbrella, 16 is a vapor deposition source, and 17 is a mask. In addition, the board | substrate 12 in Fig.2 (a) has shown the state by which the base material 13 (transparent base material 10) was set to the board | substrate jig | tool 14, as shown in FIG.2 (b).

In general, in the vacuum vapor deposition method, as shown in FIG. 2A, the substrate 12 in the chamber is provided on the vapor deposition umbrella 15, and film formation is performed by rotating the substrate 12 together with the vapor deposition umbrella 15.
In this embodiment, a mask 17 as shown in FIG. 3 is provided in parallel to the substrate 12 at a position separated from the substrate 12 by an arbitrary distance on the evaporation source 16 side of each substrate 12. With such a configuration, the vapor deposition particles to be deposited can pass through the mask 17 and reach the substrate 12 due to the geometric positional relationship between the vapor deposition source 16 and the substrate 12 and the mask 17. I cannot reach it.
As a result, a film thickness distribution in the concentration changing region that continuously changes between the two single concentration regions is obtained.
Here, when the substrate 12 and the mask 17 are brought into close contact with each other at the time of vapor deposition, a sharp (discontinuous) boundary is obtained between a portion where the film is attached and a portion where the film is not attached. On the other hand, the boundary portion becomes blurred as the distance between the substrate 12 and the mask 17 increases.

FIG. 4 shows the relationship between the width of the density change region (density change width) and the spatial distance (GAP distance) between the substrate 12 and the mask 17.
According to FIG. 4, when the concentration is changed with a width of 0.1 mm or more and 0.3 mm or less as in this embodiment, it is preferable to provide a GAP distance of 0.2 mm or more and 0.6 mm or less. Recognize.
By using such a technique, as shown in FIG. 1, an ND having a density change region in which the density is continuously changed at the boundary between two different density areas of the single density area 1 and the area 2. A filter was manufactured.
In the above description, the case where a thin film is formed on a substrate by a vacuum deposition method has been described. However, the ND filter of the present invention is not limited to such a vacuum deposition method, and a sputtering method, an inkjet printing method, or the like is also applied. can do.
In addition, since these film-forming methods are generally known, the description is abbreviate | omitted here.

Next, manufacturing conditions for the ND filter of this embodiment will be described.
First, two masks as shown in FIG. 3 were installed on the deposition source side on each film formation substrate, and the layers from the first layer to the outermost layer in the film configuration shown in FIG. 5 were formed by vacuum deposition. As the substrate 13, a PET substrate having a thickness of 75 μm was used.
The vacuum deposition method was selected because the film thickness can be controlled relatively easily and a film having very little scattering in the visible light wavelength region can be formed.
As the material of the base material, PET having high heat resistance (glass transition point Tg), high transparency in the visible light wavelength region, and low water absorption was selected.
Regarding the substrate, polycarbonate or norbornene resin may be used.
Next, the mask provided on each substrate was removed from the chamber, and the outermost layer was formed under the condition of λ / 4 (λ: 540 nm) with an optical film thickness n × d (where n is the refractive index and d is the mechanical film thickness). .
The refractive index n of the outermost layer film was selected to be 1.5 or less in the visible wavelength range. Specifically, MgF ₂ was used.
Here, if the mask as shown in FIG. 3 is used from the first layer to the outermost layer and the film thickness is changed for all the layers, the antireflection conditions are not met.
As a result, the reflectance increases, and “ghost phenomenon” and “flare phenomenon” occur as image quality problems. Considering this, the mask was removed from the outermost layer, and the film was formed so that the film thickness on the entire surface of the substrate was equal.

Next, a light quantity reduction device using the ND filter manufactured in this way will be described.
The size of the light receiving element of the photographing apparatus to which the light quantity diaphragm is attached is ½ inch, which is a general solid-state image sensor size of a video camera.
The aperture diameter was assumed to be Φ5 mm. In general, a photographing optical system of a photographing apparatus such as a video camera uses a light amount diaphragm device that adjusts a light amount by changing an aperture diameter formed by a plurality of diaphragm blades.
In such a light quantity diaphragm device, in order to prevent the aperture diameter from becoming too small, a diaphragm blade and an ND filter for attenuating the light quantity of light passing through the diaphragm aperture are used in combination, and is configured as shown in FIG. .
In FIG. 6, 4 is an ND filter, and 5 and 6 are aperture blades.
When the amount of light is controlled using the diaphragm blades 5 and 6 and the ND filter 4 as shown in FIG. 6, for example, a hall element and a detection circuit placed in the vicinity of a diaphragm blade driving motor (not shown) and an ND filter driving motor. The driving control method is used.
At that time, grasp the output voltage of each Hall element according to the rotation of the rotor in the motor and the relationship between the position of the diaphragm blade and ND filter in advance, and drive the motor while monitoring the output voltage of the Hall element Control.

Here, if the step ND filter and the gradation ND filter in which the density change at the density boundary part is discontinuous are changed, and the light amount is compared at the position where the output voltages of the Hall elements are equal, depending on the position of the ND filter, There was a case where there was a difference of 0.5 Ev or more.
As described in the above problem, this is due to the fact that there is a difference between the change in the amount of transmitted light due to the continuous density change of the gradation ND filter and that of the step ND filter.
On the other hand, when the step ND filter in which the density change at the density boundary part is discontinuous and the ND filter of the present embodiment in which the density change region has a width of 0.2 mm to 0.3 mm are compared, the difference in light amount is the largest. It was about 0.09 EV, which was not a problem.
This is because even if there is a difference in the amount of transmitted light due to variations in the position of the density change region, the area is smaller than the area of the aperture diameter, so that the level does not become a problem.

In the control system used in this experiment, the aperture diameter was reduced by the diaphragm blades from the open position (F number 2.0) to about F number 3.0 (FIG. 7A).
On the other hand, from about F number 3.0 to about F number 10 (converted light intensity is converted into F value), the movement of the diaphragm blades is fixed (therefore, the diaphragm blades remain at the position of about F number 3.0). .
Then, an ND filter having two density regions enters the opening to attenuate the light (FIG. 7 (b)), and at about F number 10, the density changing region comes out of the opening and the dark portion is the entire surface of the opening. (Fig. 7 (c)).
After that, the movement of the ND filter was stopped, and only the diaphragm blades were driven (see, for example, Japanese Patent Laid-Open No. 2000-106649 for such a drive system).
At the point of about F number 3.0 where the relationship between the operation of the ND filter and the amount of light was tested, the aperture area by the diaphragm blades was 7.1 mm ² , and the diagonal of the square aperture shape was 3.77 mm.

At this time, the moving direction of the ND filter is substantially the direction of the diagonal line. The density boundary portion (density change region) has a density gradient in the moving direction of the ND filter, and has no density change in the direction orthogonal to the moving direction.
The ratio of the density change region to the area of the opening is 5.26% when the width is 0.1 mm, 10.4% when the width is 0.2 mm, and 15.5% when the width is 0.3 mm.
Since the density change region moves relative to the opening, the area and area ratio of the opening change. The ratio of the density-changing region to the area of the opening is a value when the density-changing region is almost at the center where the influence of the transmitted wavefront phase difference is most likely to occur.

If the width of the region where the density changes continuously is less than 0.1 mm, when the density change region is in the vicinity of the end of the aperture opening, the height of the diaphragm blade is high. The shape of the opening formed between the single density region of density is similar to that at the time of small aperture.
As a result, image degradation is increased due to the influence of diffraction and transmitted wavefront phase difference. In order to eliminate these influences, a density change region of at least 0.1 mm was necessary.
In addition, when a 0.4 mm density change region that is not affected by the transmitted wavefront phase difference and diffraction is provided, the configuration is close to that of a gradation ND filter, so that an exposure error becomes large under the same experimental conditions as described above.

Here, the difference (exposure amount error EV) of the transmitted light amount of the light amount diaphragm device due to the error between the appropriate opening area and the actual opening area under the same conditions is expressed by the following equation.
Log (S2 / S1) / Log2 = Exposure amount error EV
S2 = actual aperture area S1 = appropriate (target) aperture area.
This expression indicates that the transmitted light amount (exposure amount) changes by 1 EV when the aperture area is doubled or halved.

Usually, in a video camera, a digital still camera, or the like using a solid-state image pickup device such as a CCD, it is said that the maximum allowable error is ± 0.15 EV, preferably within ± 0.1 EV.
Therefore, substituting ± 0.15 EV into the above equation,
Log (S2 / S1) /Log2=±0.15EV
S2 / S1 = 1.11, 0.90
It becomes.
In other words, the actual aperture area may vary up to 11% when the aperture aperture is large with respect to the appropriate aperture position and 10% when the aperture aperture is small.
This is an allowable exposure amount error when the stop is composed of only a portion having a transmittance of 0% and a portion having a transmittance of 100%, as in a case where, for example, a normal diaphragm blade forms a stop.
If an area in which the density continuously changes is provided on this boundary, the density is continuously increased so that the change in the amount of transmitted light (exposure amount) due to the existence of the area falls between + 11% and −10%. The allowable upper limit of the area of the region that changes to is as follows.
In other words, the allowable upper limit of the area of the region where the density continuously changes is 22% in consideration of allowing the increase of the exposure amount to 11%.
However, in consideration of allowing the reduction of the exposure amount to 10%, it is up to 20%.

Actually, since the ND filter is used to form the diaphragm, it is not completely shielded from light. However, as described above, the ND filter having the above-mentioned problem is used in the normal light quantity diaphragm device. High concentration of about 10% to 30%.
Therefore, the result almost similar to this equation is shown. In addition, since the ND filter having a low concentration hardly causes problems such as diffraction, it is not necessary to apply the present invention.
Furthermore, the exposure error can theoretically be reduced to zero by setting the midpoint of the region where the density changes continuously to the center position of the aperture opening.
However, considering the manufacturing method of the continuously changing region, it is technically difficult to prevent the light quantity control method from becoming difficult. It is desirable to restrict.

In other words, when the area of adjacent single density regions within the aperture diameter where the ratio that affects the exposure amount is maximized is substantially the same, the area of the region where the density continuously changes (density change region) is The aperture area of the aperture may be at least 20%.
That is, if the width of the density change region is set so that the area of the density change region in the opening is within 20% of the opening area, the exposure amount error is within ± 0.15 EV. Therefore, it can be controlled by the same control circuit as the control circuit of the light quantity diaphragm device provided with the conventional type step ND filter.
Incidentally, while the exposure amount error is 0.09 EV in the light quantity diaphragm using the ND filter of this embodiment, the allowable error of the calculated aperture area without the ND filter is 6.44%.
The maximum allowable area of the region in which the density of the ND filter of this embodiment continuously changes is 12.9%, which is about twice the above value with respect to the opening area (the maximum allowable width is about 0.25 mm). It almost agrees with the calculation result.
Therefore, when the exposure error is allowed up to 0.15 EV, the allowable maximum area of the area where the density continuously changes is 20% of the opening area, and the width of the area where the density continuously changes is about You may extend to 0.4 mm.
Therefore, the allowable range of the width of the region having the density change at the density boundary portion is 0.1 mm or more, and the allowable upper limit area of the density change region is substantially the same as the area in the aperture opening of the adjacent density region. 20% of the aperture area at the time. The area of the density change region is more preferably 15% or less of the aperture area of the aperture.
In this embodiment, the ND filter having two densities has been described. However, the same applies to the case of having three or more densities.

Next, an embodiment in which the light quantity stop device including the ND filter of the present invention is applied to an optical apparatus (video camera) will be described with reference to FIG.
In FIG. 8, reference numeral 1 denotes a photographing optical system having lens units 1A to 1D. A solid-state image sensor 2 such as a CCD receives an image formed by the photographing optical system 1 and converts it into an electric signal. Reference numeral 3 denotes an optical low-pass filter. The photographing optical system 1 has a light amount diaphragm device including the ND filter 4 and the diaphragm blades 5 and 6 shown in FIG.

According to the structure of the above Example, the ND filter which can improve the resolution can be provided.
Further, by using the light quantity reduction device using this in an optical apparatus having a solid-state imaging device and a photographing optical system, it is possible to achieve labor saving in development and manufacturing of a control circuit.
That is, the control circuit of the light quantity diaphragm device may be the same when developing both a model of the same series with a conventional step ND filter and a model with the ND filter according to the present invention. .
As a result, it is possible to achieve labor saving in the development and manufacture of the control circuit.

The density is continuously changed at the boundary between the two density areas in the ND filter area 1 and the ND filter area 2 having a transparent substrate and a single density area , which is applied to the diaphragm apparatus according to the first embodiment of the present invention. The figure which shows the structural example of the ND filter for light quantity diaphragms which formed the density | concentration change area | region. The simple figure which shows the structure in the chamber in the vacuum evaporation machine explaining the Example of this invention. The figure for demonstrating arrangement | positioning of the principle board | substrate and mask at the time of producing the density | concentration change area | region in the Example of this invention. The graph showing the relationship between the density | concentration change width and GAP amount for demonstrating the Example of this invention. Sectional drawing which shows the structural example of ND film | membrane filter applied to the aperture_diaphragm | restriction apparatus of the Example of this invention. Configuration diagram der Ru wing roots view of the throttle device. The figure for demonstrating operation | movement of the ND filter in the aperture_diaphragm | restriction apparatus of the Example of this invention. It is a principal part schematic of the Example of an optical instrument.

Explanation of symbols

1: Shooting optical system 1A, 1B, 1C, 1D: Lens unit 2: Solid-state imaging device 3: Optical low-pass filter 4: ND filter 5: Diaphragm blade 6: Diaphragm blade 10: Transparent substrates 11a, 11b, 11c, 11d: ND film 12: substrate 13: base material 14: substrate jig 15: vapor deposition umbrella 16: vapor deposition source 17: mask

Claims (2)

An aperture member that forms an opening;
An ND filter for attenuating the amount of light passing through the opening;
The ND filter is
A first region having a certain concentration of ND film;
A second region having an ND film having a constant concentration different from that of the first region;
A concentration change region provided between the first region and the second region;
The concentration changing region has an ND film whose concentration continuously changes from the concentration of the first region to the concentration of the second region,
The width of the concentration change region is such that when the areas of the first region and the second region are the same in the opening, the area of the concentration change region in the opening is 20% of the area of the opening. A diaphragm device characterized in that the width is set to be as follows. An optical system comprising the diaphragm device according to claim 1 ;
An optical apparatus comprising a solid-state imaging device that receives an image formed by the optical system.

Images